Epoxy adhesive composition

ABSTRACT

Epoxy-type adhesive compositions comprising glycidyl polyether of a dihydric phenol, filler, a flexibilizer and a curing agent, preferably, a mixture of an amine hardener and a rigidifying tertiary amine catalyst. Enhancement of special properties is obtained by admixing a silane or silicone adhesion promoter. The use of a low cost amine hardener is made possible by the addition of an aromatic dihydroxy compound and/or a high boiling coal-tar fraction.

United States Patent [191 Smeal v EPOXY'ADHESIVE COMPOSITION [75]Inventor: Thomas W. Smeal, Franklin Twp.,

' Westmoreland County, Pa.

[73] Assignee: United States Steel Corporation, Pittsburgh, Pa.

22 Filed: Jan. 19,1972

[21] Appl. No.: 219,174

[52] US. Cl. 260/33. 6 EP, 260/24, 260/37 EP 51 Int. Cl C08g 51/28 58Field of Search 260137 EP, 33.6 FP,

[56] References Cited UNITED STATES PATENTS 3,532,653 10/1970 Smeal260/37 E? X Primary E xaminerLew is T. Jacobs AttorneyGene Harsh et al.

[ ABSTRACT Epoxytype adhesive compositions comprising glycidyl polyetherof a dihydric phenol, filler, a flexibilizer and a a curing agent,preferably, a mixture of an amine hardener and a rigidifying tertiaryamine catalyst. Enhancement of special properties is obtained byadmixing a silane or silicone adhesion promoter. The use of a low costamine hardener is made possible. by the addition of an aromaticdihydroxy compound and/or a high boiling coal-tar fraction. Y

10 Claims, No Drawings EPOXY ADHESIVE COMPOSITION BACKGROUND OF THEINVENTION This invention relates to modified epoxy compositions havingapplication as adhesives hardening at room temperature with high tensileshear and peel strengths over a wide service-temperature range andrelative insensitivity to dirty surfaces. More particularly, theinvention relates to an epoxy-resin composition modified with filler anda flexibilizer and further modifiable with a silane or silicone adhesionpromoter, an aromatic dihydroxy compound, and/or a highboiling coal-tarfraction. The compositions are cured at room temperature with a novelmixture of an amine hardener, a rigidifying catalyst, and an aromaticdihydroxy compound and/or a high-boiling coal-tar fraction.

Modified epoxy resin compositions are well known in the art and aredescribed, for example, in U.S. Pat. Nos. 2,500,499, 3,033,088 and3,062,77l. Among the preferred resins are glycidyl polyethers ofdihydric phenols having epoxy equivalencies greater than. 1. The resinsmay be modified by fillers, high boiling oil fractions and a variety ofother materials to enhance their properties. A great number of curingagents have been specified to solidify the compositions at roomtemperature. These prior art compositions, when used as adhesives, havegood properties at ambient temperatures, but they lose most of theirtensile and peel strengths at temperatures near the extremes of about 67and 180F. Roomtemperature hardened polymers resistant to thistemperature range are usually rigid and poor in resistance to peelstresses. Flexible polymers have good peel resistance but are notresistant to temperature extremes, especially elevated temperatures.Additionally, nonporous substrates, for example, metal sheets must -becleaned carefully before application of such adhesive compositions.

ln U.S. Pat. No. 3,532,653, epoxy-resin adhesives containing a novelcombination of chemical curing agents, relatively large amounts ofspecific mineral fillers and flexibilizers, small amounts of silane orsilicone adhesion promoters and/or relatively large amounts ofhigh-boiling coal-tar fractions are disclosed. These compositions,however, required the use of expensive flexibilizing primary polyaminehardeners.

SUMMARY OF THE INVENTION I have now discovered that the adhesivequalities of percent of a filler such as talc, silica, dolomite,anhydrous calcium sulfate and aluminum silicate, about 1 to 7 percent ofa flexibilizer such as vpoly(vinylalkyl ether), where the alkyl groupcomprises from one to five carbon atoms, rosin ester, solid polyamideresin (i.e., the condensation product of an organic diamine and anorganic dibasic acid such as the condensation product of hexamethylenediamine and adipic acid), or a copolymer of styrene and butadiene. Acuring agent 10 for the polyether comprises approximately astoichiometric amount of a mixture of an amine hardener and arigidifying tertiary amine catalyst as more particularly defined below.To this composition may be added between about 0.5 and 2 percent of asilane or silicone adhesion promoter, about 0.5 to 10 percent of anaromatic dihydroxy compound, and about 10 to 40 percent of acoal-tar-fraction boiling between about 500 and 900F. All percentagesare by weight of the total composition including any additives.

DETAILED DESCRIPTION A preferred group of epoxy ethers useful in myinvention is prepared by reacting a dihydric phenol with epi chlorhydrinin alkaline solution. The products comprise ethereal oxygen and glycidylgroups in such quantity that the products have 1,2-epoxy equivalency inthe average molecule greater'than one. By epoxy equivalency, referenceis made to the average number of 1.2-

epox'y groups p CHIIEQ.

contained in an average molecule or the ether. The

products are of resinous character and are either solid or liquidmaterials at normal temperature (20 30C Any of the various dihydricphenols may be used in preparing the glycidyl ethers, and whichpreferably con- 5 hydroxyphenyl)-2,2-butane, bis-(4-hydroxy2-methylphenyl)-2,2-propane, bis-(hydroxy2-tertiarybutyl phe--ny1)-2,2-propane, bis- (2-dihydroxynaphthyl)- methane, and l,5-dihydroxynaphthalene. The products may be represented by the formula:

epoxy-resin adhesive compositions may be maintained 5 or improved andthe cost considerably lowered by replacing expensive flexibilizing aminehardeners with inexpensive rigidifying primary polyamine hardeners usedin conjunction with an aromatic dihydroxy com-.

droxy compound yields an adhesive composition that is flexible and hashigh peel strength.

My compositions comprise between 15 and percent ofa glycidyl polyetherofa dihydric phenol having an epoxy equivalency greater than l, about 25to wherein n is an integer, preferably from 0 to 7, and R represents adivalent hydrocarbon radical of a dihydric phenol. A preferred phenol isbis-phenol A, Le. bis-(4- hydroxyphenyl)-2,2-propane. Preferred epoxyethers for use in the invention are those having epoxy values no lessthan 0.20 (pyridinium chloride method), and melting points up to aboutC. (Durran's mercury method). A glycidyl ether resin will contain atleast one epoxy group'and usually less than two per molecule.

V Epoxide equivalent weight is defined as the number of grams of resincontaining 1 gram equivalent of epoxide.

Successful adhesives were prepared with commercially available epoxyresins in the above classification, for example, Epotuf 37-139-(diglycidyl ether of bis-phenol A, epoxy equivalent 182 to 195,viscosity 5,000 to l0,000 centipoises) and Epotuf 37-140 (diglycidyl13,500 centipoises), Epi-rez 508 (molecularly distilled diglycidyl etherof bis-phenol A, epoxy equivalent weight 171 to 177, viscosity 3,600 to5,500 centipoises), Epi-rez 510 (liquid diglycidyl ether of bisphenol A,epoxy equivalent weight 180 to 200, viscosity 10,000 to 16,000centipoises), DER 330(diglycidylether of bis-phenol A, epoxy equivalentweight 182 to 189, viscosity 7,000 to 10,000 centipoises), and DER 331(liquid diglycidyl ether of bis-phenol A, epoxy equivalent weight 186 to192, viscosity 1 1,000 to 14,000 centipoises). All viscosities are at25C.

Preferred fillers for my adhesives have been found to be talc,silica'(preferably ground to pass 200 mesh), dolomite (a mixture ofcalcium and magnesium carbonates), anhydrous calcium sulfate, andaluminum silicate. A balance of desirable properties is secured-with amixture of approximately equal parts by weight of dolomite and aluminumsilicate.

Only a relatively few of a relatively large number of properties withoutdegrading hightemperature properties. These flexibilizers are poly(vinylalkyl ether) where the alkyl group comprises one to five carbon atoms,rosin esters, solid polyamide resins and copolymers of styrene andbutadiene. The poly(vinyl alkyl ether) compounds are polymers havingfrom about to about 4,000 repeating units; preferably 100 to 2,000 andthe alkyl group has from one to five carbon atoms. All of thesecompounds have a molecular weight of about 500 to about200,000;'preferably about 5,000 to 100,000. In the specification andclaims it is to be understood that the term flexibilizer" means amaterial developed to impart flexibility to a resinous composition.

Theprior art has proposed a relatively large number of room-temperaturecuring agents. For purposes of my invention, and in the specificationand claims, primary and secondary amines are classified as hardeners andtertiary amines are rigidifying catalysts. Most primary and secondaryamine hardeners are not useful in my invention.

The products resulting from the use of an aminehardener as opposed to arigidifying catalyst would appear to be quite dissimilar since thepreferred primary amine-hardeners combine with the epoxy resins inaddition-type reactions to give products having little heat resistance.On the contrary, rigidifying catalysts usually do not enter into thereaction but serve to open the epoxy rings to permit epoxy to epoxybonding. The productsare very hard and rigid with excellent heatresistance. Surprisingly, and quite unexpectedly, l have found synergismin combining a hardener and a rigidifying catalyst, since the desirableproperties thereof were retained and the undesirable properties thereofwere overcome with a suitable amount of an aromatic ing a chain of 2carbon groups with two to. seven carbon atoms per group, an ether'linkbetween the groups and an amine group on each end of the chain (e.g.,liquid diamines having the general formula z iz) O I u) NH '2 wherein nhas a value of 2 to 7 inclusive and x has a value of 2 to 7 inclusive.For example, suitable liquid diamines have the formulae C H MO o zz zThe preferred aromatic dihydroxy compounds are resorcinol andbisphenol-A. Preferred rigidifying tertiary amine catalysts aretri(dimethyl amino methyl) phenol, dimethyl amino methyl phenol andbenzyldimenthylamine. These 1 catalysts arecommercially availablerespectively as DMP-30, DMP-lO and BDMA.-lt is necessary that thetertiary amine catalyst have at least six carbon atoms, and it ispreferred that the tertiary amine catalyst have six to 20 carbon atoms,

' the most preferred tertiary amines are those that boil above about85C. Relative to the epoxy resin an approximately stoichiometric orequivalent amount of curing agent mixture gives satisfactory results;broadly, between about 0.90 and 1.10 and preferably between about 1.00and 1.05 times the. stoichiometricamount of a mixture. It has been foundthat the relative proportions of hardener and catalyst in the mixtureare extremely critical. For example, a stoichiometric amount of aflexibilizing primary polyamine hardener produced an adhesive weak at77F and higher temperatures, but with excellent low-temperatureipeelstrength. Replacing about 30 to 50 percent of the hardener with astoichiometrically equivalent amount'of a rigidifying tertiary aminecatalyst greatly. improved the adhesive strength at 77F and above,without significantly lowering the low-temperature peel strength. Thisis quite surprising, since it would be expected that the lowtemperaturepeel strength would gradually decline as the proportion of catalystincreases. It has been found, however, that low-temperature peelstrength is relatively unaffected until about 50 percent replacementwith catalyst. Thereafter, this strength deteriorates quite rapidly andis practically non-existent with about a 60 percent. replacement. It hasbeen found that the curing agent mixture may be between about and 50percent hardener and 30 and 50 percent catalyst, preferably betweenabout 67 and 60 percent hardener and 33 and 40 percent catalyst.

A stoichiometric amount of hardener is defined as the amount supplyingexactly one active hydrogen for each epoxy group in a given mass ofresin. Actually, there is no corresponding stoichiometric amount for acatalyst. There are, however, manufacturers recommendations for anamount to provide an adequate de-' gree of curing within a reasonableperiod of time. In the specification and claims such amounts areconsidered equivalent" or stoichiometric."

It has been found that the broadlimits for a basic adhesive compositioncomprises in percent by weight between about 15 and 60 percent resin,between about 25 and 70 percent filler, between about 1 and 7 percentflexibilizer, between about 0.5 and 14 percent. amine hardener, betweenabout 0.3 and 3 percent rigidifying tertiary amine catalyst and betweenabout 0.5 and 10 percent aromatic dihydroxy compound and/or 10 to 40percent high-boiling aromatic oil. Preferably, a composition comprisesbetween about 18 and 50" percent resin, between about 30 and 60 percentfiller, between about 2 and 5 percent flexibilizer, between about 2.5and l 1 percent hardener, between about 0.5 and 2 percent catalyst, andbetween about 1 and 4 percent aromatic dihydroxy compound and/or to 30percent of high-boiling aromatic oil with a coal-tar oil boiling at 670to 850F being preferred.

When the above described amine hardener is used in the adhesivecomposition without added aromatic hydroxy compound or aromatic oil, lowpeel strength due to decreased flexibility results. The addition of thearomatic hydroxy compound increases the peel strength to above thatobtained when a flexibil-izing amine hardener is used. The addition ofaromatic oil alone increases the peel strength somewhat but for mostapplications not to a sufficient level.- The preferred adhesivecomposition contains suitable amounts of both aromatic hydroxy compoundand aromatic oil.

It has been found that the hereinabove described compositions may beimproved by the addition of other materials. The above compositions showimproved strength properties, moisture resistance and handlingproperties by the addition thereto of relatively small amounts ofcertain silanes or silicones. 1n the specification and claims, referencewill be made to those silanes and silicones which are commerciallyavailable materials, developed specifically as adhesion promoters, assilane and silicone adhesion promoters. Broadly useful additions arebetween about 0.2 and 2 percent by weight. The preferred range isbetween 0.4 and 1.2 percent. Useful commercially available materialsinclude Silane A-l100 (gamma-aminopropyltriethoxysilane), Silane A-186(3,4-epoxy-cyclohexylethyltrimethoxysilane), Silane A-l87(glycidoxylpropyltrimethoxysilane) and Paint Additive 21. The latter isdesignated a silicone by the manufacturer, e.g. N-beta- (am in'oethyl)-gamma-aminopropyltrimethoxysilane The above basic composition with orwithout the addition thereto of silane or silicone adhesion promoters,become surprisingly insensitive to dirty and to galvanized surfaces, andmore moisture resistant and tacky when there is added thereto arelatively large amount of a coal-tar fraction, boiling between about500 and 900F', more preferably, boiling between about 670 and 850F.Additions may be between about 20 and 40 percent by weight of the totalcompositiommore preferably between about 25 and 30 percent of the totalcomposition of from 1.1 to 1.7 times the weight of Epoxy resin is acondensation product of bisphenol-A and epichlorohydrin with an epoxideequivalent of 185 to 195 and a viscosity at 77F of 5,000 to 10,000centipoises.

Catalyst ASP-400 is aluminum silicate, grade ASP 400.

Gellant is the reaction product of dodecyl amine with anhydrous aluminumsilicate (bentonite) prepared as in Example 2 of USP 2,531,427.

Flexible polyamine hardener is H NCH,-CH CH (OCH CH CH,) -NH Catalyst istri(dimethylaminomethyl) phenol.

Adhesion promoter NH2CH2CH2NH(CHg)3Si(OCH3) in n-butyl alcohol.

Polyamine X hardener is H N(C H )O(C H )NH 1n all of the followingexamples, the parts are by weight unless otherwise specificallyindicated.

EXAMPLES- 1 3 Example 1 shows the excellent adhesive strength resultsobtained when a composition employing a flexibilizing primary polyaminehardener having a chain of 4 carbon groups with three carbon atoms pergroup, an ether link between the groups, and an amine group on each endof the chain is used. Example 2 shows that when a primary polyaminehardener (polyamine X) having only 2 carbon groups with four carbonatoms those of Example 1 if an aromatic dihydroxy compound (resorcinol)is included. The adhesives in these'examples were all cured for 3minutes in a 400F forceddraft oven.

Composition Ex. 2 Epoxy resin 48.0 48.0 46.7 Filler, talc 34.2 34.2 34.9Flexibilizer, poly(vinyl ethyl ether 4.0 4,0 3.9 Gellant 2.0 2.0 2.0Flexible polyamine hardener 8.7 Polyamine X hardener 8.7 7.9 Catalyst1.9 1.9 1.5 Adhesion promoter. 1.2 1.2 *1 .2 Resorcinol 1.9 AdhesiveStrength Properties Ex. 1 Ex. 2 Ex. 3

' Lap-shear strength, psi,

at -67F 4100 3850 3800 77F 3150 3350 3050 F 3050 3150 3300 77F after 28days in water 3450 3500 3300 180'Degree peel strength, ppi, at 67F 50 4060 77F 35 25 45 180F '35 25 Climbing-drum peel strength. ippi, at 77F 2515 25 EXAMPLES 4 AND 5 These examples demonstrate that, in the presenceof a large amount of coal-tar boiling between about 670 and 845F, thereis the unexpected result that polyamine X will produce adhesivestrengths equivalent to those obtained with the flexibilizing polyamineof Example 1 upon curing both compositions'for 10 days at roomtemperature.

Composition. Example 4 Example 5 Epoxy resin 19.37 19.37 Dolomite AA22.60 22.60 Gellant 0.20 0.20 Coal-tar oil 27.45 27.45 Flexibilizer,poly(viny| ethyl ether) 3.23 3.23 ASP-400 22.41 22.41 Flexible polyaminehardener 3.49 Polyamine X hardener 3.49

Adhesion promoter 0.47 0.47 Adhesive Strength Properties Example 4Example 5 Lap-shear strength, psi, at 40F 3250 2700 at 77F 3250 3050 atl45F I750 I750 at 77F after 28 days in water 2950 2950 ISO-Degree peelStrength, ppi, at --40F 12 30 at 77F 35 30 at l45F 30 20 Climbing-drumpeel strength. ippi, at 77F 2s 20 I claim:

1. An epoxy type adhesive composition comprising 15 to 60 weight percentglycidyl polyether of a dihydric phenol having an epoxy equivalencygreater than 1, 25 to 60 weight percent tiller, 1 to 7 weight percentflexibilizer, selected from the group consisting of rosin esters, solidpolyamide resins, copolymers of butadiene and styrene, and poly(vinylalkyl ethers) having a molecular weight of from about 5,000 toabout 200,000 wherein the alkyl group has from one to live carbon atoms,0.5 to 10 weight percent monoor di-nuclear aromatic dihydroxy compoundand 0.8 to 17 weight percent two-component curing agent comprising 0.5to 14 weight percent of an amine hardener and 0.3 to 3 weight percent ofa rigidifying tertiary amine catalyst having from six to 20 carbon atomsand a boiling point above about 85C wherein said amine hardener isselected from compounds having the formula n having a value of 2 to 7and x having a value of2 to 2. The composition of claim 1 comprising 18to weight percent glycidyl polyether of a dihydric phenol, 30 to 60weight percent filler, 2 to 5 weight percent flexibilizer, l to 4 weightpercent aromatic dihydroxy compound, 2.5 to 11 weight percent aminehardener and 0.5 to 2 weight percent rigidifying tertiary aminecatalyst.

3. The composition of claim 1 comprising 10 to 40 weight percent of anaromatic oil boiling in the range of 500 900F.

4. The composition of claim 1 comprising 15 to 30 weight percent ofcoal-tar oil boiling in the range of 670 850F.

5. The composition of claim 1 comprising 0.2 to 2 weight percentadhesion promoter selected from silicone and silane adhesion promoters.

6. The composition of claim 1 wherein the flexibilizer is poly(vinylethyl ether).

- 7. The composition of claim 3 wherein the filler is a mixture ofdolomite and talc, the flexibilizer is poly (vinyl ethyl ether), and thearomatic dihydroxy compound is resorcinol.

8. The composition of claim 1 wherein the empirical formula of the aminehardener is C H N O.

9. The composition of claim 1 wherein the empirical formula of the aminehardener is C H N O.

2. The composition of claim 1 comprising 18 to 50 weight percentglycidyl polyether of a dihydric phenol, 30 to 60 weight percent filler,2 to 5 weight percent flexibilizer, 1 to 4 weight percent aromaticdihydroxy compound, 2.5 to 11 weight percent amine hardener and 0.5 to 2weight percent rigidifying tertiary amine catalyst.
 3. The compositionof claim 1 comprising 10 to 40 weight percent of an aromatic oil boilingin the range of 500* - 900*F.
 4. The composition of claim 1 comprising15 to 30 weight percent of coal-tar oil boiling in the range of 670* -850*F.
 5. The composition of claim 1 comprising 0.2 to 2 weight percentadhesion promoter selected from silicone and silane adhesion promoters.6. The composition of claim 1 wherein the flexibilizer is poly(vinylethyl ether).
 7. The composition of claim 3 wherein the filler is amixture of dolomite and talc, the flexibilizer is poly (vinyl ethylether), and the aromatic dihydroxy compound is resorcinol.
 8. Thecomposition of claim 1 wherein the empirical formula of the aminehardener is C8H20N2O.
 9. The composition of claim 1 wherein theempirical formula of the amine hardener is C9H22N2O.
 10. The compositionof claim 1 wherein the empirical formula of the amine hardener isC10H24N2O.